The present invention relates to the art of medical diagnostic imaging. It finds particular application in conjunction with computed tomography (CT) scanners, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other rotating gantry applications.
Generally, CT scanners have a defined examination region or scan circle in which a patient, or subject being imaged is disposed. A thin fan beam of radiation is transmitted across the examination region from an radiation source, such as an x-ray tube, to an oppositely disposed array of radiation detectors. The x-ray tube and associated power supply and cooling components are rotated around the examination region while data is collected from the radiation detectors. Rotation of the radiation source is often achieved by mounting the radiation source to a rotating gantry which is rotated on a stationary gantry.
The sampled data is typically manipulated via appropriate reconstruction processors to generate an image representation of the subject which is displayed in a human-viewable form. Various hardware geometries have been utilized in this process. In third generation scanners, both the source and detectors rotate around the subject. In a fourth generation scanner, the x-ray source rotates and the detectors remain stationary. The detector array typically extends 360xc2x0 around the subject in a ring outside of the trajectory of the x-ray tube.
In previously developed CT scanners, commonly the rotating gantry is supported on the stationary gantry via a large diameter mechanical bearing including rolling elements or balls interposed between two raceways. The bearing was typically on the order of three quarters of a meter to two meters in diameter. Mechanical bearings typically have a small amount of play or clearance between the races and the rotating elements. The mechanical play permits the x-ray tube and detectors in a third generation scanner to move axially and radially and permits the plane of rotation to cant. Accurate reconstruction, typically to a resolution on the order of millimeters is dependant upon acquiring data from accurately resolved positions of the source and the detectors.
In helical volume scanning, CT fluoroscopy or other real time imaging techniques, and high speed imaging, the x-ray tube gantry rotates continuously at high speed. However, with increased rotational speed of the rotating gantry, noise levels associated with mechanical bearings reach unacceptable levels. In continuously rotating systems, friction related heating can restrict the length of scans. Moreover, the accompanying fiction causes wearing of parts in physical contact with one another thereby incurring increased play and noise, disadvantageous maintenance requirements, and a limited lifetime.
The present invention contemplates a new and improved gantry suspension technique which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a diagnostic imaging apparatus is provided. An x-ray source is mounted on a rotating gantry. The rotating gantry or a stationary gantry includes at least one smooth, annular bearing race. Fluid bearing pads are mounted to the other of the gantries, having a porous face that contacts the smooth annular bearing race. A pump supplies a bearing fluid to the pads to be ejected therefrom.
In accordance with another aspect of the present invention, A diagnostic imaging apparatus is provided. A plurality of individual bearing pads are mounted to a stationary gantry, at least some of them being mounted for individual radial adjustment. A rotating gantry including at least one bearing race is separated from the bearing pads by a thin layer of air as it rotates. An x-ray tube is mounted on the rotating gantry.
In accordance with another aspect of the present invention, a method of diagnostic imaging is provided. A rotating gantry is rotated about an imaging region. Fluid bearings are created between the rotating gantry and a plurality of fluid bearing pads. A bias of at least some of the bearing pads is adjusted. An image representation of a subject in an imaging region is reconstructed by irradiating the subject and reconstructing detected radiation.
One advantage of the present invention is faster CT tri scanner speeds and correspondingly reduced scan times.
Another advantage of the present invention is quieter CT scanner operation.
Another advantage of the present invention is extended bearing life with reduced maintenance.
Another advantage resides in a CT scanner with a larger gantry and bore.
Yet another advantage resides in the simplicity of the support structure.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.